The present invention relates to a device for resisting the tendency of a railway car truck to lozenge or get out of square. More particularly the invention relates to a novel configuration of the interfaces between the friction shoe and its reaction surfaces on the side frame and bolster.
The type of railway car truck to which the present invention relates comprises, generally, spaced side frame members each having an opening arranged to resiliently support opposite ends of a bolster. The side frame members are substantially parallel to one another, and the bolster is normally perpendicular to the plane of both side frames.
Occasionally, however, one side frame member, while remaining parallel to the other member, may get slightly ahead of the other member. In this condition, which is known as lozenging, the bolster is no longer perpendicular to the side frame members. Lozenging is a result of the railway car truck hunting back and forth across the tracks rather than rolling straight with respect to the tracks. This hunting or lateral instability generally occurs with a truck of the type herein described at speeds above about 60 km/hr under light load conditions. Lozenging decreases the truck hunting threshold speed and lateral stability as compared to squared trucks.
The lateral instability may result in increased wheel flange and track wear, and lozenging is therefore an important operating concern of the railroad industry. It has been observed that the speed threshold at which lozenging occurs can be increased with a squared truck.
It is a primary object of the present invention to provide a railway car truck constructed and arranged to overcome the difficulties encountered heretofore and thereby improve the safe and efficient operation thereof.
According to the present invention this is accomplished through the friction shoe arrangement. Friction shoes are provided to frictionally engage both the side frame column and bolster. The degree of squaring or resistance to lozenging is dependent on the restraining moment developed by the friction shoes. Therefore, an increase in restraining moment results in an increased truck hunting threshold speed.
Heretofore, although truck designers have illustrated friction shoes as having contact surfaces with some appropriate manufacturing tolerance, there has been no predetermined attempt to control initial contact areas to develop the maximum restraining moment.
This invention discloses several ways in which the restraining moment may be maximized and better retained as wear of the friction shoe develops.